First introduced to oilfield operations in the early 1960's, coiled tubing is now an essential component of hydrocarbon production. Coiled tubing is used in applications ranging from well cleanout to directional drilling. Available in sizes ranging from 1″ to 4.5″, coiled tubing strings are carried on reels and injected into a wellbore using a coiled tubing injector unit. A typical coiled tubing injector unit 5 is depicted in FIG. 1. The typical unit includes a goose-neck support 3, a rotary transmission assembly, parallel drive-chains 7 carrying grippers, skates and a hydraulic system. (The transmission assembly, grippers, skates and hydraulic system are not shown in detail in FIG. 1.) Those skilled in the art are familiar with the components and operation of the unit 5 depicted in FIG. 1.
The series of grippers carried by the chains provide the sole direct support for holding the coiled tubing in place or moving the tubing. The grippers are arranged in opposing pairs to secure the coiled tubing string between the injector-head chains. The hydraulic system applies pressure to the skates which in turn force the grippers toward each other thereby securing the coiled tubing between the grippers. Additionally, the hydraulic drive system drives the chains to feed the coiled tubing string into the well or pull the tubing out of the well.
A typical gripper includes a carrier secured to the chain and a gripping shoe supported by the carrier. From time to time, the gripping shoe must be replaced due to damage or to accommodate a change in tubing diameter or insertion of a downhole tool. Therefore, a need exists for a carrier/gripping shoe assembly which permits replacement of the gripping shoe without replacing the entire chain assembly.